Below the belt and Hush-hush

Below the belt adjective - Disregarding the rules (from the notion of an illegal low blow in boxing).

Hush-hush and below the belt are semantically related. In some cases you can use "Hush-hush" instead an adjective phrase "Below the belt".

Hush-hush adjective - Not known or meant to be known by the general populace.

Below the belt and hush-hush are semantically related. Sometimes you can use "Below the belt" instead an adjective phrase "Hush-hush".